U.S. patent application number 09/729193 was filed with the patent office on 2001-06-07 for plasma cvd apparatus and plasma cvd method.
This patent application is currently assigned to NEC Corporation. Invention is credited to Yuda, Katsuhisa.
Application Number | 20010003014 09/729193 |
Document ID | / |
Family ID | 18395137 |
Filed Date | 2001-06-07 |
United States Patent
Application |
20010003014 |
Kind Code |
A1 |
Yuda, Katsuhisa |
June 7, 2001 |
Plasma CVD apparatus and plasma CVD method
Abstract
A remote plasma CVD apparatus is disclosed, in which oxygen gas
18 is supplied to a high frequency wave applying electrode 1 to
cause reaction of oxygen radicals and oxygen molecules 21 with
monisilane gas 19, which is introduced into part of a substrate
processing zone R outside oxygen plasma 22. The apparatus comprises
a plasma confining electrode 20, which has jetting holes for
supplying monosilane gas 19 to the substrate processing zone R. The
electrode 20 is spaced apart from a substrate 3 (i.e., deposition
substrate) by a distance no longer than about 1,500 .lambda..sub.g
of the mean free path in the substrate processing zone R at the
time of film formation. The member 20 has a hollow structure, and
accommodates dispersing plates (i.e., a first and a second
dispersing plate) for uniformalizing monosilane gas (i.e., neurtral
gas) in it. Thus both of suppression of excessive progress of gas
phase chemical reaction and homogeneous film formation in a remote
plasma CVD apparatus for forming film by gas phase chemical
reaction are realized.
Inventors: |
Yuda, Katsuhisa; (Tokyo,
JP) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET 2ND FLOOR
ARLINGTON
VA
22202
|
Assignee: |
NEC Corporation
|
Family ID: |
18395137 |
Appl. No.: |
09/729193 |
Filed: |
December 5, 2000 |
Current U.S.
Class: |
427/562 ;
118/723E |
Current CPC
Class: |
C23C 16/452 20130101;
H01J 37/32357 20130101; C23C 16/45565 20130101; C23C 16/5096
20130101; C23C 16/45591 20130101 |
Class at
Publication: |
427/562 ;
118/723.00E |
International
Class: |
B05D 003/14; C23C
016/509 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 7, 1999 |
JP |
348157/1999 |
Claims
What is claimed is:
1. A plasma CVD apparatus comprising a substrate processing zone
with a deposition substrate disposed therein, a plasma generating
zone for generating plasma of first gas, and a plasma confining
electrode for separating the substrate processing zone and the
plasma generating zone and confining the first gas and having holes
for passing first gas containing neutral radicals from the first
gas plasma, wherein: the plasma confining electrode has a hollow
structure, accommodates gas dispersing plates for uniformalizing
second gas in the plasma confining electrode, and has holes for
introducing the second gas into the substrate processing zone to
form a desired film on the deposition substrate by gas phase
chemical reaction of the first gas containing neutral radicals and
the second gas with each other; and the vertical distance between
the plasma confining electrode and the deposition substrate is no
longer than 1,500 times the mean free path .lambda..sub.g of blend
gas of neutral radicals and the second gas in the substrate
processing zone at the time of film formation.
2. The plasma CVD apparatus according to claim 1, wherein a
plurality of parallel dispersing panels are disposed as the
afore-said dispersing plates in the plasma confining electrode.
3. A plasma CVD film forming method comprising: a first step of
forming plasma of first gas in a plasma generating zone; a second
step of confining the plasma in the plasma generating zone with a
plasma confining electrode member; a third step, in which the
plasma confining electrode member passes through holes formed
therein neutral radicals from the plasma to a substrate processing
zone; a fourth step, in which the plasma confining electrode member
supplies uniformalized second gas, with dispersing plates disposed
in the member for uniformalizing the second gas, to the substrate
processing zone with a deposition substrate disposed therein; and a
fifth step of forming a desired film on the deposition substrate by
gas phase chemical reaction of the first gas containing neutral
radicals and the second gas; wherein: the vertical distance between
the plasma confining electrode member and the deposition substrate
is no longer than about 1,500 times the mean free path
.lambda..sub.g in the substrate processing zone at the time of film
generation.
4. A plasma CVD apparatus comprising a substrate processing zone
with a deposition substrate disposed therein, a plasma generating
zone for generating plasma of first gas, and a plasma confining
electrode for separating the substrate processing zone and the
plasma generating zone and confining the first gas and having holes
for passing first gas containing neutral radicals from the first
gas plasma, wherein: the plasma CVD apparatus further comprises a
gas introducing member disposed between the plasma confining
electrode member and the deposition substrate and having a
plurality of holes, through which second gas is introduced into the
substrate processing zone to form a desired film on the deposition
substrate by gas phase chemical reaction between the first gas
containing neutral radicals and the second gas; and the gas
introducing member has a hollow structure, accommodates dispersing
plates for uniformalizing the second gas in it and is vertically
spaced apart by a distance no longer than about 1,500 times the
mean free path .lambda..sub.g in the substrate processing zone.
5. The plasma CVD according to claim 4, wherein a plurality of
parallel dispersing plates are disposed as the afore-said
dispersing planes in the gas introducing member.
6. A plasma CVD film forming method comprising: a first step of
forming plasma of first gas in a plasma generating zone; a second
step of confining the plasma in the plasma generating zone with a
plasma confining electrode member; a third step, in which the
plasma confining electrode member supplies first gas containing
neutral radicals through its holes from the plasma to a space
between the plasma confining electrode member and a gas introducing
member; a fourth step, in which the gas introducing member passes
first gas containing neutral radicals through its holes to the
substrate processing zone with a deposition substrate disposed
therein; a fifth step, in which the gas introducing member supplies
uniformalized second gas to the substrate processing zone with
dispersing plates disposed in it for uniformalizing the second gas;
and a sixth step of forming a desired film on the deposition
substrate by gas phase chemical reaction between the first gas
containing neutral radicals and the second gas; wherein: the gas
introducing member is spaced apart from the deposition substrate by
a vertical distance no longer than about 1,500 times the mean free
path .lambda..sub.g in the substrate processing zone.
Description
BACKGROUND OF THE INVENTION
[0001] This application claims benefit of Japanese Patent
Application No. 11-348157 filed on Dec. 7, 1999, the contents of
which are incorporated by the reference.
[0002] The present invention relates to plasma CVD (chemical vapor
deposition) apparatus and plasma CVD method using the same and,
more particularly, to a remote plasma CVD apparatus which separates
a plasma forming zone and a substrate processing zone and also to a
method of forming a large area, homogeneous and dense film by
remote plasma CVD.
[0003] Among various types of plasma CVD apparatus for forming a
film on a substrate while suppressing plasma damage are a remote
plasma CVD apparatus, which separates a plasma forming zone and a
substrate processing zone R. The CVD film formation using this
remote plasma CVD apparatus implements a very important technique
as thin film forming process for manufacturing high reliability
devices and high performance devices.
[0004] As for remote plasma CVD apparatus, which can be used for a
large area substrate processing, such as a switching transistor
forming process and a drive circuit transistor forming process for
a large area flat panel display, or as a process of processing a
large diameter silicon wafer, a parallel plate remote plasma CVD
apparatus is disclosed in, for instance, Japanese Laid-Open Patent
No. 5-21393.
[0005] FIG. 7 shows a parallel plate plasma CVD apparatus in this
prior art remote plasma CVD apparatus. As shown, the apparatus
comprises a plasma confining electrode 8, which is obtained by
using a mesh plate having a plurality of holes and disposed between
a high frequency wave applying electrode 1 and a back electrode 2,
on which a substrate is set.
[0006] In this parallel plate remote plasma CVD apparatus, plasma 6
is confined between the high frequency wave applying electrode 1
and the plasma confining electrode 8.
[0007] Such gas as neutral radicals 4 is supplied from large area
homogenous plasma confined between the two parallel plates, i.e.,
high frequency wave applying electrode 1 and plasma confining
electrode 8, to a substrate processing zone R. The apparatus thus
features that a large area uniform distribution of neutral radicals
4 for the like supplied to the substrate processing zone R is
obtained within the top surface of substrate 3, so that a thin film
forming process can be carried out uniformly over the substrate 3,
which may have a large area as well.
[0008] In this prior art apparatus, the plasma confining electrode
8, i.e., mesh plate, has radical passing holes 5 for passing
radicals 4 therethrough and also neutral gas jetting holes 9, which
are formed near the holes 5 and serve to jet out neutral gas 10
from them. A large area uniform film depositing process is thus
possible as process of forming a film on the substrate 3 even in
the case of utilizing gas phase reaction between the radicals 4 and
the neutral gas 10.
[0009] When carrying out film formation (i.e., film forming
process) involving gas phase chemical reaction in the substrate
processing zone R in the parallel plate remote plasma CVD apparatus
as shown in FIG. 7, first gas plasma (i.e., plasma 6) which
contributes to the reaction is formed, and radicals (i.e., radicals
4) of excited first gas and non-excited first gas are supplied from
the plasma through the radical passing holes 5 in the plasma
confining electrode 8 to the substrate processing zone R for
reaction second gas supplied from the neutral gas jetting holes 9
to form a film formation precursor, which is necessary for the film
formation.
[0010] As an example, when carrying out silicon oxide film
formation by reaction between monosilane (SiH.sub.4) and oxygen
(O.sub.2) , oxygen is supplied as first gas, and monosilane as
second gas.
[0011] The plasma confining electrode 8 has large numbers of
radical passing holes 5 and neutral gas jetting holes 9. Thus, if
the second gas (i.e., neutral gas 10) is supplied uniformly from
the large number of neutral gas jetting holes 9, gas phase reaction
can be brought about uniformly over the top surface of substrate 3
in the substrate processing zone R, and a homogeneous film can be
formed on the substrate surface.
[0012] Owing to the above features, the parallel plate remote
plasma CVD apparatus is considered to be promising as method of
forming silicon oxide (SiO.sub.2) film and silicon nitride
Si.sub.3N.sub.4 or Si.sub.xN.sub.y layers as gate insulating film
of thin film transistor on large area glass substrate, method of
forming amorphous silicon film as active layer or gate electrode of
thin film transistor on the large area glass substrate, method of
forming silicon oxide film or silicon nitride film as inter-layer
insulating film of transistor element on the large area glass
substrate, and so forth.
[0013] The plasma confining electrode 8 in the above prior art
apparatus (disclosed in Japanese Patent Laid-Open No. 5-21393), has
a hollow structure having the neutral gas jetting holes 9, which
are, as described before, formed near the radial passing holes 5
for surface uniform supply of neutral gas 10.
[0014] In the plasma confining electrode 8 having the hollow
structure, as shown in a side and a top view of the electrode 8 in
FIGS. 8 and 9, the radical passing holes 5 and the neutral gas
jetting holes 9 are formed independently (or separately) of one
another. Thus, radicals 4 and neutral gas 10 are not mixed and
reacted with one another in the space in hollow electrode 8.
[0015] As shown in FIG. 9 or 10, in the prior art apparatus neutral
gas 10 is supplied to the hollow plasma gas confining electrode 8
from the outside of the evacuated chamber. Specifically, neutral
gas 10 is supplied to the space in the electrode 8 from a neutral
gas supply duct line, which is provided on an end surface of the
electrode 8.
[0016] In the gas supply method in this prior art case, the
pressure in the space in the plasma confining electrode 8 is
substantially the same as the film formation pressure in the
substrate processing zone R, i.e., several ten to several hundred
Torr.
[0017] Therefore, as schematically shown in FIG. 11, neutral gas 10
is mostly jetted out from neutral gas jetting holes 9 in the
neighborhood of the connection juncture between neutral gas supply
duct line 12 and the plasma confining electrode 9, and are jetted
out at lower rates from jetting holes 9 remoter from the duct line
12. This is a drawback in that it is difficult to jet out neutral
gas 10 uniformly over the surface of the substrate 3.
[0018] In this circumstance of difficulty of uniformly jetting out
neutral gas 10 over the substrate surface is difficult, it is
conceivable to increase the distance D of the plasma confining
electrode 8 for jetting out neutral gas 10 therefrom from the
substrate 3 in order to form a homogeneous film within the
substrate surface.
[0019] In the case when gas phase chemical reaction is brought
about between the second gas (i.e., neutral gas 10), which is
supplied non-uniformly over the substrate surface in the substrate
processing zone, with the first gas, reaction product (i.e., film
formation precursor that is generated as a result of gas phase
chemical reaction is distributed non-uniformly over the substrate
surface in the neighborhood of the second gas supply port.
[0020] With the increased distance D as noted above, however,
sufficient time is provided for the second gas and the reaction
product to be dispersed in directions parallel to the surface of
the substrate 3 until reaching of the substrate 3. Thus, uniform
distribution is obtainable within the surface of the substrate 3 at
the time of reaching the substrate 3.
[0021] In this film forming method, it is possible to obtain the
more uniform distribution the greater the distance D between the
plasma confining electrode 3 and the substrate 3 with respect to
the width W of the CVD chamber.
[0022] As an example, when carrying out film formation on a glass
substrate of 500 mm.times.600 mm, the width W of the CVD chamber is
about 800 mm, and in this case sufficient uniformalizing effect is
obtainable with the same length, (i.e., about 100 mm) between the
plasma confining electrode and the substrate.
[0023] In the film formation by the gas phase chemical reaction,
however, if the distance D between the plasma confining electrode 8
with the neutral gas jetting holes 9 for jetting neutral gas 10
therefrom and the deposition base substrate (i.e., substrate 3) is
increased, the gas phase reaction between the first gas containing
neutral gas radicals and the second gas proceeds excessively to
result in process of growth of particles (i.e., film formation
precursor) in the gas phase in the substrate processing zone R and
consequent deposition of the grown particles on the substrate
surface, thus resulting in the generation of a coarse film.
[0024] As an example, in the formation of a silicon oxide film by
gas phase chemical reaction of monosilane and oxygen, SiO.sub.x
particles (i.e., film formation precursor) are grown in the gas
phase in the substrate processing zone R.
[0025] Such coarse film as formed in the above way is high in
defect density, high in leak current and low in dielectric strength
and, therefore, can not be used as thin film transistor gate
insulating film and the like.
SUMMARY OF THE INVENTION
[0026] The present invention was made in view of the above
background, and it seeks to provide a remote plasma CVD apparatus
and a remote plasma CVD method capable of providing film formation
precursor, which permits dense and surface uniform film deposition
on deposition base substrate without particle growth due to
excessive gas phase chemical reaction in the film formation in a
remote plasma CVD method based on the gas phase chemical
reaction.
[0027] According to an aspect of the present invention, there is
provided a plasma CVD apparatus comprising a substrate processing
zone with a deposition substrate disposed therein, a plasma
generating zone for generating plasma of first gas, and a plasma
confining electrode for separating the substrate processing zone
and the plasma generating zone and confining the first gas and
having holes for passing first gas containing neutral radicals from
the first gas plasma, wherein: the plasma confining electrode has a
hollow structure, accommodates gas dispersing plates for
uniformalizing second gas in the plasma confining electrode, and
has holes for introducing the second gas into the substrate
processing zone to form a desired film on the deposition substrate
by gas phase chemical reaction of the first gas containing neutral
radicals and the second gas with each other; and the vertical
distance between the plasma confining electrode and the deposition
substrate is no longer than 1,500 times the mean free path
.lambda..sub.g blend gas of neutral radicals and the second gas in
the substrate processing zone at the time of film formation.
[0028] A plurality of parallel dispersing panels are disposed as
the afore-said dispersing plates in the plasma confining
electrode.
[0029] According to another aspect of the present invention, there
is provided a plasma CVD film forming method comprising: a first
step of forming plasma of first gas in a plasma generating zone; a
second step of confining the plasma in the plasma generating zone
with a plasma confining electrode member; a third step, in which
the plasma confining electrode member passes through holes formed
therein neutral radicals from the plasma to a substrate processing
zone; a fourth step, in which the plasma confining electrode member
supplies uniformalized second gas, with dispersing plates disposed
in the member for uniformalizing the second gas, to the substrate
processing zone with a deposition substrate disposed therein; and a
fifth step of forming a desired film on the deposition substrate by
gas phase chemical reaction of the first gas containing neutral
radicals and the second gas;wherein: the vertical distance between
the plasma confining electrode member and the deposition substrate
is no longer than about 1,500 times the mean free path
.lambda..sub.g in the substrate processing zone at the time of film
generation.
[0030] According to other aspect of the present invention, there is
provided a plasma CVD apparatus comprising a substrate processing
zone with a deposition substrate disposed therein, a plasma
generating zone for generating plasma of first gas, and a plasma
confining electrode for separating the substrate processing zone
and the plasma generating zone and confining the first gas and
having holes for passing first gas containing neutral radicals from
the first gas plasma, wherein: the plasma CVD apparatus further
comprises a gas introducing member disposed between the plasma
confining electrode member and the deposition substrate and having
a plurality of holes, through which second gas is introduced into
the substrate processing zone to form a desired film on the
deposition substrate by gas phase chemical reaction between the
first gas containing neutral radicals and the second gas; and the
gas introducing member has a hollow structure, accommodates
dispersing plates for uniformalizing the second gas in it and is
vertically spaced apart by a distance no longer than about 1,500
times the mean free path .lambda..sub.g in the substrate processing
zone.
[0031] A plurality of parallel dispersing plates are disposed as
the afore-said dispersing planes in the gas introducing member.
[0032] According to still other aspect of the present invention,
there is provided a plasma CVD film forming method comprising: a
first step of forming plasma of first gas in a plasma generating
zone; a second step of confining the plasma in the plasma
generating zone with a plasma confining electrode member; a third
step, in which the plasma confining electrode member supplies first
gas containing neutral radicals through its holes from the plasma
to a space between the plasma confining electrode member and a gas
introducing member; a fourth step, in which the gas introducing
member passes first gas containing neutral radicals through its
holes to the substrate processing zone with a deposition substrate
disposed therein; a fifth step, in which the gas introducing member
supplies uniformalized second gas to the substrate processing zone
with dispersing plates disposed in it for uniformalizing the second
gas; and a sixth step of forming a desired film on the deposition
substrate by gas phase chemical reaction between the first gas
containing neutral radicals and the second gas wherein: the gas
introducing member is spaced apart from the deposition substrate by
a vertical distance no longer than about 1,500 times the mean free
path .lambda..sub.g in the substrate processing zone.
[0033] Other objects and features will be clarified from the
following description with reference to attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a schematic side view showing a parallel plate
remote plasma CVD apparatus as a first embodiment of the present
invention;
[0035] FIG. 2 is a schematic sectional view showing a plasma
confining electrode accommodating dispersing plates in the first
embodiment of the present invention;
[0036] FIGS. 3A and 3B are schematic plan views showing an upper
and a lower plate of the plasma confining electrode accommodating
dispersing plates in the first embodiment of the present
invention;
[0037] FIGS. 4A and 4B are schematic plan views showing the
dispersing plates in the first embodiment of the present
invention;
[0038] FIG. 5 is a view showing leak current characteristics of
deposited silicon oxide films;
[0039] FIG. 6 is a schematic side view showing a parallel plate
remote plasma CVD apparatus as a second embodiment of the present
invention;
[0040] FIG. 7 is a schematic side view showing a prior art parallel
plate remote plasma CVD apparatus;
[0041] FIG. 8 is a schematic sectional view showing a plasma
confining electrode having a hollow structure in the prior art
apparatus;
[0042] FIG. 9 is a schematic plan view showing the plasma confining
electrode having the hollow structure in the prior art;
[0043] FIG. 10 is a schematic side view showing the prior art
parallel plate remote plasma CVD apparatus for describing a method
of supplying neutral gas to the hollow plasma confining electrode
from the outside of vacuum chamber; and
[0044] FIG. 11 is a schematic sectional view illustrating the
manner of gas jetting from the hollow plasma confining electrode in
the prior art apparatus.
PREFERRED EMBODIMENTS OF THE INVENTION
[0045] Preferred embodiments of the present invention will now be
described with reference to the drawings.
[0046] FIG. 1 is a schematic schematic sectional view showing the
construction of an embodiment of remote plasma CVD (chemical vapor
deposition) apparatus according to the present invention. An
embodiment of the present invention will now be described in
detail. The embodiment of the present invention will now be
described in connection with silicon oxide film formation in an
oxygen/silane parallel plate remote plasma CVD apparatus as an
example with reference to the Figure. Elements like those in the
prior art example are designated by like reference numerals, and
are not described.
[0047] As basically shown in FIG. 1, the parallel plate flat remote
plasma CVD apparatus comprises a vacuum chamber capable of being
evacuated, a high frequency power supply 13, a high frequency wave
applying electrode 1, a back electrode 2 supporting a substrate 3,
a plasma confining electrode 20, which has radial passing holes for
passing gas containing neutral radicals therethrough and is
electrically grounded, and a neutral gas supply duct line 12 for
supplying neutral gas (for instance monosilane 19) into the plasma
confining electrode 20 from an end thereof.
[0048] The plasma confining electrode 20 accommodates dispersing
members having radical passing holes and neutral gas jetting
holes.
[0049] FIG. 2 is a schematic sectional view having the plasma
confining electrode 20 having the dispersing plates. In the Figure,
a plurality of dispersing plates, i.e., a first and a second
dispersing plate 23 and 24 in this embodiment, for uniformly
dispersing monosilane gas (i.e., neutral gas) 19, are provided
(i.e., disposed) in the apace defined between an upper and a lower
plate 26 and 27 in the plasma confining electrode 20.
[0050] In FIG. 2, monosilane gas 19 is supplied to the space
between the upper plasma confining electrode plate 26 and the first
gas dispersing plate 23, then uniformalized through holes 9A in the
first dispersing plate 3 and then through holes 9B in the second
gas dispersing plate 24, and then jetted through neutral gas
jetting holes 9 in the plasma confining electrode lower plate 27 in
a plane uniform fashion toward the base 3.
[0051] The holes 9A, 9B and neutral gas jetting holes 9 are
provided separately (i.e., independently) of the radical passing
holes 5 in the plasma confining electrode 20 such that oxygen
radicals and oxygen molecules 21 are not mixed with monosilane gas
19. To this end, the radical passing holes 5 are formed as
continuous holes 5 by walls isolating them from the zone, in which
monosilane gas is present.
[0052] While in the case of FIG. 2 two dispersing panels, i.e., the
first and second dispersing plates 23 and 24, are shown, it is also
possible to use only a single dispersing plate or two or more
dispersing plates.
[0053] The diameter of the opening of the radical passing holes 5,
which are continuous between the upper and lower plasma containing
electrode plates 26 and 27 set to the length roughly less than
double the plasma device length of generated oxygen plasma 22.
[0054] FIGS. 3A and 3B are plan views showing the upper and lower
plasma containing electrode plates 26 and 27.
[0055] Referring to FIG. 3A, the upper plasma confining electrode
plate 26 has radical passing holes 5, which are provided at uniform
intervals and serve to pass gas containing neutral radicals through
them.
[0056] Referring to FIG. 3B, in the lower plasma confining
electrode plate 27 the radical passing holes 5 are open at
predetermined intervals for passing the gas containing neutral
radicals. The plate 27 also has neutral gas jetting holes 9 formed
at uniform intervals and at positions not coincident with the
radical passing holes 5.
[0057] FIGS. 4A and 4B are plan views showing dispersing plates,
i.e., first and second dispersing plates 23 and 24. The two
dispersing plates, i.e., the first and second dispersing plates 23
and 24, correspond to corresponding first and second dispersing
plates 23 and 24.
[0058] Referring to FIG. 4A, the first dispersing plate 23 is
penetrated by the radical passing holes 5 spaced apart at uniform
intervals for passing gas including neutral radicals, and it also
has neutral gas passing holes 9, which are formed at uniform
intervals in its predetermined area Q near the center at positions
non-coincident with the radical passing holes 5.
[0059] Referring to FIG. 4B, the second dispersing plate 24 has the
radical passing holes 5 spaced apart at uniform intervals for
passing neutral radicals, and it also has neutral gas passing holes
9, which are formed at uniform intervals in its predetermined area
P near the center at positions non-coincident with the radical
passing holes 5.
[0060] In the case when the two dispersing plates, i.e., the first
and second dispersing plates 23 and 24, are aligned to each other
in their installation in the plasma confining electrode 20, the
area P covers and broader than the area Q.
[0061] In other words, the second dispersing plate 24 has the
neutral gas passing holes 9, which are provided not only at the
positions corresponding to those in the first dispersing plate 23
but also in an outside area.
[0062] Although it is possible to provide neutral gas passing holes
at uniform intervals over the entire dispersing plate area, by
contriving the disposition of holes of a plurality of dispersing
plates in FIGS. 4A and 4B as described before, it is possible to
prevent jetting-out of gas at high rates into the substrate
processing zone R near the neutral gas supply duct line 12 and thus
obtain more plane uniform supply of neutral gas (for instance,
monosilane gas 19) over the surface of the substrate 3.
[0063] Furthermore, it is possible to dispose the two dispersing
plates, i.e., the first and second dispersing plates 23 and 24, in
the plasma confining electrode 20 such that their like holes, i.e.,
the holes 9A and 9B, through which monosilane (i.e., neutral gas)
19 flows, are deviated from one another in plan view (i.e., not in
vertical lines).
[0064] Now, a method of forming a silicon oxide film on the surface
of the substrate 3 with one embodiment of the remote plasma CVD
apparatus will now be described with reference to FIGS. 1 to 4A and
4B.
[0065] Oxygen gas 18 is introduced into the high frequency wave
applying electrode 1 in the CVD chamber in an evacuated state
(under a predetermined pressure), and is then supplied uniformly
from the bottom of the electrode 1 toward the plasma confining
electrode 20. Thus, glow discharge of the oxygen gas is brought
about in the space between the electrode 1 and the plasma confining
electrode 20 (accommodating the first and second dispersing plates
23 and 24 shown in FIG. 4).
[0066] As a result of the glow discharge, oxygen plasma 22 is
generated, which is efficiently confined between the high frequency
wave applying electrode 1 and the plasma confining electrode
20.
[0067] As a result, a situation is set up that the plasma density
of the oxygen plasma 22 is about 10.sup.10 cm.sup.-3 while that in
the space between the high frequency wave applying electrode 20 and
the back electrode 2 (or substrate 3) is about 10.sup.5 to 10.sup.6
cm.sup.-3.
[0068] This situation indicates that although electrons, oxygen
atom ions, oxygen molecule ions, oxygen atom radicals, oxygen
molecule radicals and oxygen molecules are present in the oxygen
plasma 22, electrons and ions introduced in the zone outside the
plasma are substantially negligible.
[0069] Thus, in the space 22 outside the plasma 22, oxygen atom
radicals, oxygen molecule radicals and non-excited oxygen molecules
undergo reaction with the monosilane gas 19 jetted out into the
substrate proceding zone R and thus contribute to the silicon oxide
film formation.
[0070] Oxygen radicals and oxygen molecules 21 are dispersed
through the radical passing holes 5 into the substrate processing
zone R for gas phase chemical reaction with the monosilane gas 19
jetted out from the neutral gas jetting holes 9.
[0071] As a result of the gas phase chemical reaction, silicon
oxide precursor (i.e., film formation precursor), such as
SiO.sub.x, SiO.sub.xH.sub.y and SiH.sub.y is formed and deposited
on the surface of the substrate 3, thus forming a silicon oxide
film on the substrate 3.
[0072] The plasma confining electrode 20 is spaced apart from the
substrate 3 by a distance D (i.e., vertical distance), which is set
to be shorter than about 1,500 (excluding 0) times the mean free
path .lambda..sub.g of the blend gas of oxygen (i.e., oxygen
radicals and oxygen molecules 21) and monosilane in the substrate
processing zone R. This distance D has an effect of preventing
excessive progress of the gas phase chemical reaction. It is thus
impossible that the silicon oxide precursor, such as SiO.sub.x,
SiO.sub.xH.sub.y and SiH.sub.y, undergoes particle growth to a
particle size in the gas phase in the substrate processing zone
R.
[0073] For example, under conditions with the gas temperature of
300.degree. C. and the chamber pressure of 250 mTorr, the mean free
path .lambda..sub.g of the oxygen/monosilane blend gas is about 60
.mu.m, and in this case the distance D between the plasma confining
electrode and the substrate may be set to 90 mm or below.
[0074] FIG. 5 shows leak current characteristics obtained in an
experimental example of silicon oxide film formation. In this
example, silicon oxide films were formed by setting, as experiment
conditions, the substrate temperature to 300.degree. C., the
pressure in the substrate processing zone R to 250 mTorr, the flow
rate of oxygen supplied through the high frequency wave applying
electrode 1 to the plasma zone to 800 sccm, and the flow rate of
monosilane gas supplied to the neutral gas supply duct line 12 to 5
sccm, and used as gate insulating film of MOS (metal/oxide
film/semiconductor).
[0075] As is seen from FIG. 5, the leak current density is greatly
different with samples, which were obtained by setting the distance
D between the plasma confining electrode 20 and the substrate 3 to
300 and 60 mm, respectively.
[0076] The film sample obtained by setting the distance D between
the plasma confining electrode 20 and the base 3 to 60 mm, has a
leak current characteristic close to that of thermal silicon oxide
film and satisfactory, and it also has such electric insulating
characteristic and breakdown voltage that it can be used as gate
insulating film or inter-layer insulating film of thin film
transistor.
[0077] On the other hand, the film sample obtained by setting the
distance D between the plasma confining electrode 20 and the base 3
to 300 mm, has such a leak current characteristic that leak current
flows highly from low electric field range, and its dielectric
insulating characteristic and breakdown voltage are such low that
it can not be used as gate insulating film and inter-layer
insulating film of thin film transistor.
[0078] As a further experimental condition in this example, the
mean free path .lambda..sub.g of the oxygen/monosilane blend gas in
the substrate processing zone R was set to about 60 .mu.m.
[0079] This means that the distance D of 300 mm between the plasma
confining electrode 20, in which the electric insulating
characteristic and breakdown voltage are inadequate, and the
substrate 3 corresponds to about 5,000 times the mean free path
.lambda..sub.g.
[0080] On the other hand, the distance D of 60 mm between the other
plasma confining electrode 20, in which the electric insulating
characteristic and breakdown voltage are adequate, corresponds to
about 1,000 times the mean free path .lambda..sub.g.
[0081] In the case of the long distance D between the plasma
confining electrode 20 and the substrate 3 corresponding to about
5,000 times the mean free path .lambda..sub.g, it is estimated that
the gas phase chemical reaction of oxygen radicals and oxygen
molecules 21 with monosilane gas 19 takes place excessively, thus
resulting in deposition of particles, which are grown as particle
growth in the gas phase in the substrate processing zone R, and
consequent coarse film formed on the surface of the substrate
3.
[0082] In contrast, in the case of the distance D between the
plasma confining electrode 20 and the substrate 3 corresponding to
about 1,000 times the mean free path g, it is estimated that the
gas phase chemical reaction of oxygen radicals and oxygen molecules
21 with monosilane gas 21 takes place not excessively, thus
restricting the particle growth in the gas phase and eliminating
deposition of silicon oxide film formation precursor in particle
form as film on the surface of the substrate 3.
[0083] As described above, in the parallel plate remote plasma CVD
the plasma density in the space between the plasma confining
electrode 20 and the back electrode 2 is very low, and it is thus
possible to suppress the plasma damage to the substrate 3 to be
very little compared to the case of the usual parallel plate plasma
CVD.
[0084] This effect is pronounced in the case when the surface of
the substrate 3 is a silicon surface forming a MOS interface.
Specifically, in the case of formation of SiO.sub.2 film on single
crystal silicon substrate by the usual parallel plate plasma CVD
the MOS surface state density is 10.sup.11 to
10.sup.12cm.sup.-2eV.sup.-1 in the neighborhood of the mid gap,
whereas in the case of silicon oxide film formation by the parallel
plate remote plasma CVD the surface density is as low as at most
10.sup.10 cm.sup.-2eV.sup.-1.
[0085] While one embodiment of the present invention has been
described in detail with reference to drawings, its specific
construction is by no means limitative, design changes and
modifications may be made without departing from the scope of the
present invention.
[0086] Parallel plate remote plasma CVD in a second embodiment of
the present invention will now be described with reference to FIG.
6. FIG. 6 is a schematic sectional view showing a parallel plate
remote plasma CVD apparatus embodying the present invention. In the
Figure, elements like those in the prior art example and the
preceding embodiment are designated by like reference numerals, and
are not described.
[0087] Referring to FIG. 6, the illustrated parallel plate remote
plasma CVD is different from the parallel plate remote plasma CVD
apparatus shown in FIG. 1 in that it comprises a gas introducing
member 29, which neutral gas (i.e., monosilane gas 19) is supplied
into from a neutral gas supply duct line 12 connected to it, and
accommodates dispersing plates for uniformalizing the gas density
before jetting-out of gas toward substrate, does not have any
plasma confining function.
[0088] Thus, the gas introducing member 29 accommodating the
dispersing plates may have radical passing holes 5 having any
diameter so long as radicals 4 can be jetted out uniformly. It is
also possible to use the member 29 without being grounded, i.e., in
an electrically floated state. It will be seen that the gas
introducing member 29 is different from the plasma confining
electrode 20 in the previous embodiment in the freedom from being
grounded and also in the diameter of the radical passing holes,
although it has the same construction.
[0089] The gas introducing member 29 is disposed between plasma
confining electrode 8 and back electrode 2, and its distance F from
substrate 3 is set to be no longer than 1,500 (excluding 0) times
the mean free path .lambda..sub.g of blend gas of oxygen (i.e.,
oxygen radicals and oxygen molecules 21) and monosilane in the
substrate processing zone R.
[0090] For the remainder, the gas introducing member 29
accommodating the dispersing plates, in the second embodiment, is
the same in construction as the plasma confining electrode 20 which
also accommodates dispersing plates.
[0091] The concept of the structure of the dispersing plates in the
gas introducing member 29 and the relationship among the number of
dispersing plates, and the distribution of the radical passing
holes in the dispersing plates and the neutral gas passing holes
therein, is the same as the concept of the dispersing plates (i.e.,
first and second dispersing plates) in the plasma confining
electrode 20 in the first embodiment.
[0092] Also, the concept of the distance F between the gas
introducing member 29 and the substrate 3 is the same as the
concept of the distance D in the plasma confining electrode 29 and
the substrate 3 in the plasma confining electrode 20 in the first
embodiment. Thus, the gas phase chemical reaction of oxygen
radicals and oxygen molecules 21 with monosilane gas 19 does not
take place excessively, thus restricting the particle growth in the
gas phase and eliminating deposition of particles as film on the
surface of the substrate 3.
[0093] In the above first and second embodiments, the present
invention was described in connection with silicon oxide film
formation using monosilane and oxygen. However, it is possible to
replace monosilane with higher degree silane such as disilane or
such liquid Si material as TEOS (tetra ethoxysilane, and it is also
possible to replace oxygen with nitrous oxide, nitrogen oxide,
etc.
[0094] Also, while the above embodiments were described in
connection with the silicon oxide film formation with the remote
plasma CVD apparatus, it is possible to obtain the same effects as
the films formed in the embodiments with films, which are formed
with plasma CVD apparatuses involving gas phase chemical reaction
with other materials such as silicon nitride film formation by
reaction of monosilane and ammonia with each other.
[0095] Furthermore, while the above embodiments were described in
connection with the parallel plate remote plasma CVD apparatus, the
present invention is applicable as well to any other type of
apparatus such as those utilizing microwave plasma, electronic
cyclotron resonant plasma, inductively coupled plasma, helicon wave
plasma, etc. insofar as the plasma CVC apparatus includes a
plurality of holes between the plasma generating region and the
substrate processing region R, and employs a plasma confining
electrode for plasma separation.
[0096] As has been described in the foregoing, with the remote
plasma CVD apparatus for forming film by gas phase chemical
reaction according to the present invention, it is possible to
suppress excessive progress of the gas phase chemical reaction and
obtain uniform concentration of neutral gas jetted out in the
outside-plasma zone over the deposition substrate.
[0097] It is thus possible, with the remote plasma CVD apparatus
according to the present invention to form a dense film free from
any particle on a large area substrate in the manufacture of gate
insulating film or inter-layer insulating film of MOS element.
[0098] Changes in construction will occur to those skilled in the
art and various apparently different modifications and embodiments
may be made without departing from the scope of the present
invention. The matter set forth in the foregoing description and
accompanying drawings is offered by way of illustration only. It is
therefore intended that the foregoing description be regarded as
illustrative rather than limiting.
* * * * *